There are known apparatus and methods for sensing the presence of media in printers along the media pathway during the performance of key operations within a printer. However, the inclusion of multiple functions within a printer occurring in rapid succession requires the use of multiple and reliable sensors to detect the presence of the sheet of print medium and to permit the continued operation of the printer.
Printers and copiers for some time have routinely employed sensors to detect the presence or absence of media to signal the operator to replenish the supply of media. However, as technologies have advanced and printing speeds have increased it has become necessary to detect more conditions more rapidly to ensure safe and efficient operation of the desk top printers now widely used in conjunction with personal computers. For example, in phase change ink printers one of the key functions involves the fusing of the ink image to the image-receiving medium. This function requires the proper timing of the feeding of the medium into a media preheater and the completion of the imaging process on a transfer drum followed by the movement of a fusing roller, such as by actuation of an eccentric shaft, to move the fusing roller against the transfer drum, thereby forming a pressure nip through which the medium is fed, to ensure that the image is both pressure and heat fused to the image receiving medium. Sensors are required to ensure that these functions are coordinated and timely initiated. Sensors can also be required to check for jams that may occur by signalling the passage or non-passage of media past specific points along the media flow path within the printer. Such sensors can be coupled to visual or audial indicators in order to alert the printer operator to media path malfunctions.
Printers, copiers, and facsimile machines are other examples of mechanically complex devices that perform multiple print producing functions. FIG. 1 shows an exemplary transfer printer 10, which is described in U.S. Pat. No. 4,538,156 issued Aug. 27, 1985 for an INK JET PRINTER. A multiple-orifice ink-jet print head 12 deposits an ink image on a surface 14 of a transfer drum 16 that is rotated by a motor (not shown) driving a drum shaft 18. A print medium 20 received from a media supply tray 22 is advanced into a nip formed between transfer drum 16 and a transfer roller 24. A solenoid 26 is energized actuating a linkage 28 that pivots an arm 30 holding transfer roller 24 such that print medium 20 is pressed in the nip between transfer drum 16 and transfer roller 24. The rotation of drum 16 draws print medium 20 through the nip, thereby transferring the ink image from drum surface 14 to print medium 20 while feeding it into an exit path 32. After print medium 20 leaves the nip, solenoid 26 is de-energized and a solenoid 34 is energized, pivoting an arm 36 holding a web roller 38 such that a drum cleaning web 40 is drawn into contact with and cleans surface 14 of transfer drum 16. The rotation of transfer drum 16 draws cleaning web 40 from a web supply spool 42 to a web take-up spool 44. After transfer drum 16 is adequately cleaned, solenoid 34 is de-energized and the above-described process may be repeated.
In practice, such printers may also include print processing functions not shown in FIG. 1, such as a print media picking function that picks a single sheet of print medium 20 from media supply tray 22, a print media transport function that transfers print medium 20 into the nip, a stripper finger engagement function that strips print medium 20 off transfer drum 16, an exit path engagement function that drives print medium 20 into exit path 32, a web take-up spool 44 driving function that provides a fresh supply of drum cleaning web 40, and a print head positioning function that provides adequate clearance between transfer drum 16 and print head 12 for periodic print head maintenance.
The above-described functions are selectively engaged by independent motive forces, actuated in a predetermined timing sequence, and in some cases at a particular angular position of transfer drum 16. Each function has a "home position" or a rotationally indexed position that must be initialized or sensed prior to each print, following a paper jam, after filling the media supply tray, or when initiating a print head maintenance process. Some functions, such as media feed may be accomplished manually or automatically, requiring interactive and alternative driving mechanisms. As a result, the above-described functions plus other reversible functions such as transfer roller engagement and print head positioning are typically powered and engaged by multiple independent motive forces, the number of which together with their associated linkages and controllers result in an unduly complex and sub-optimal printing mechanism that consumes excessive power and space and can require rapid and effective sensing mechanisms to permit effective and reliable operation.
What is needed, therefore, is a compact multiple function print processor in which the functions are monitored and controlled by a simple and effective sensor system to form an improved printing mechanism.